Optical recording employing laser makes storage and reproduction of high density information records possible, and its developments have been remarkable recent years.
As an example of optical recording, an optical disc may be mentioned. An optical disc is usually designed to irradiate a focused laser beam of about 1 .mu.m, to a thin recording layer formed on a substrate of disc shape to conduct high density information recording. The recording is carried out in such a manner that upon absorption of the laser beam energy, the irradiated portion of the recording layer will undergo a thermal deformation such as decomposition, vaporization or melting. Reproduction of the recorded information is carried out by reading the difference in the reflectance between the portion having a deformation formed by the laser beam and the portion having no such deformation.
Accordingly, the recording layer is required to efficiently absorb the energy of the laser beam, and a laser-absorbing dye is employed for this purpose.
Various structures are known for optical recording media of this type. For example, Japanese Unexamined Patent Publication No. 97033/1980 discloses the one having a single layer of a phthalocyanine type dye formed on a substrate. However, the phthalocyanine type dye is poor in the sensitivity and further has a problem such that the decomposition point is high and it is hardly vaporized. Further, its solubility in an organic solvent is very low, and thus it has a problem that it can not be used for coating by a coating method.
Further, Japanese Unexamined Patent Publications No. 11279/1983, No. 114989/1983, No. 85791/1984 and No. 83236/1985 disclose the one having a cyanine type dye as a recording layer. Such a dye has a merit that the solubility is high, and it is thereby possible to conduct coating by a coating method. However, it has a problem that it is inferior in the light fastness. Therefore, Japanese Unexamined Patent Publication No. 55795/1984 proposes to improve the light fastness by adding a quencher to this cyanine type dye, but the improvement has not yet been sufficient.
In connection with these problems, Japanese Unexamined Patent Publication No. 30090/1987 discloses complexes of certain specific monoazo compounds and metals, as media having the solubility in an organic solvent and the light resistance improved. However, these compounds have short photosensitive wavelengths and thus are poor in the sensitivity, and they are also poor in the storage stability under a high temperature high humidity condition. Thus, they have problems in their use for optical recording media.